Rabbit Proto is a print head add-on that works with RepRap printers with dual-extrusion boards. It uses a 10cc syringe to deposit conductive ink, specifically Bare Conductive’s product. Together with its firmware, Rabbit Proto lets a 3D printer lay down circuits inside an object that’s being printed, saving a lot of time and effort. The video below shows a working video game controller made straight out of a 3D printer:

Here’s another example, a 3D printed electronic puzzle.:

As if that wasn’t awesome enough, you can actually use Rabbit Proto to extrude any viscous material that fits inside its syringe. The video below shows it being used with peanut butter:

You can pre-order Rabbit Proto for $350 (USD). It comes with one syringe of conductive ink. You can also get a Rabbit Proto dual-extrusion add-on – the syringe plus a filament extruder – for $450 or a whole 3D printer equipped with the dual extrusion add-on for $2,499.